Improved splitter

Splitter now has a new split algorithm that usually results
in fewer, more evenly sized tiles.

The test generator is > 10 times faster. This allows a deeper
search for good splits. A few errors where fixed which
sometimes prohibited to find a good split, but also sometimes
helped to find one.

A new option --search-limit can be used to increase/decrease the
amount of time the splitter tries to find a good split.
The larger the input file the higher this value should be.
For planet, --search-limit=1000000 is okay, --search-limit=10000000
is better.